Oka Shigemasa served as a bushō during the Azuchi-Momoyama and early Edo periods.  He was a chief retainer of the Gamō family of the Mutsu-Aizu domain.  His common name was Hanbei.

Shigemasa was a descendant of Takeda Nobutoyo, a shugo daimyō in Wakasa Province.  His formal wife was Koishi-dono – the second daughter of Ishida Mitsunari.  His son was named Oka Kichiemon.

Shigemasa first served Gamō Ujisato.  After the death of Ujisato in 1595, he served his eldest son, Gamō Hideyuki.  After the Battle of Sekigahara, when a youthful Hideyuki returned to Aizu, Shigemasa had been appointed as a magistrate of the policies of the Toyotomi administration in the northern provinces and managed affairs of the domain.

In 1612, Hideyuki suddenly died at the age of thirty and was succeeded by his eldest son, Gamō Tadasato, at the age of ten.  His widow, Furihime (the third daughter of Tokugawa Ieyasu), served as his guardian.  She then came into a severe conflict with Shigemasa over matters of governance of the domain.  Moreover, this reignited the internal conflicts that erupted after the death of Ujisato so her father (Ieyasu) and older brother (Tokugawa Hidetada) were concerned about disruption in the clan, taking steps including dispatching a censor to go over the laws.  This state of affairs culminated in Ieyasu summoning Shigemasa to Sunpu Castle and ordering him to commit seppuku the following year.

Shigemasa’s son, Kichiemon, received protection from Machino Yukikazu (who served as a deputy to Shigemasa), and wed Yukikazu’s daughter who gave birth to a daughter named Ofuri (Jishōin).  Ofuri became an adopted daughter of Kasuga-no-tsubone, and, as a consort of Tokugawa Iemitsu (the third supreme shōgun of the Edo bakufu) gave birth to Iemitsu’s eldest daughter named Chiyohime (Reisen-in).  This lineage continues to the present day.